Plunger electromagnet with anti-stick means separating the poles and operating a utilization device



Jan. 17, 1967 B. K. M REYNOLDS PLUNGER ELECTROMAGNET WITH ANTI-STICKMEANS SEPARATING THE POLES AND OPERATING A UTILIZATION DEVICE 2Sheets-Sheet 1 Filed March 15, 1965 IN VE N TOR Boone K. M Reyno/ds Jan.17, 1967 'B K. M REYNOLDS 3,299,380

v PLUNGER ELECTROMAGNET WITH ANTI-STICK MEANS SEPARATING THE POLES ANDOPERATING A UTILIZATION DEVICE llll Filed March 15,1965 2 Sheets-Sheet 2Ill 303 am V U 307 PRlOR ART-- United States Patent York Filed Mar. 15,1965. Ser. No. 439,812 6 Claims. (Cl. 335-420) The invention relates tocore assemblies for tractive electromagncts and more particularlyconcerns a nonferromagnetic actuating pin aguided for longitudinalmovement by one piece of a two-piece conical-faced ferromagnetic core.The actuating pi-n has a flared truncated conical end within the coil ofthe electromagnet to provide a residual gap that mates with thetruncated conical ends of the two-piece core.

In known core assemblies for tractive electromagnets, the bestforce-stroke characteristic curves have been obtained with conical-facedcores. In one such arrangement, the core assembly comprises twoconica-1-faced ferromagnetic pole pieces, one of which is movable andthe other stationary. A nonferromagnetic actuating pin in the form of astraight pusher pin is guided by means of a hole in the stationary pole.Upon energization of the electromagnet, the movable pole or plunger isattracted to the stationary pole, thereby driving the pusher pin toactuate external mechanism. Problems exist, however, in the provision ofa residual gap to prevent continued engagement of the plunger with thestationary pole due to residual magnetism in the poles afterde-energization of the electromagnet. In small electromag-nets, it isespecially difficult to control the width of the residual gap by anarrangement that may be economically manufactured. Air gaps aredifficult to adjust and maintain at correct and consistent widths. Gapsof nonferromagnetic material which are coated or secured in some othermanner to the face of one of the pole pieces, necessitate an extra stepin the manufacture of the electromagnet. Another serious difficultyfound is that repeated impact of the plunger against the pusher pincauses a mushroom deformation at the end of one or both parts. Suchdeformation often becomes suflicient to cause the mushroomed end ofeither or both the pusher pin and plunger to jam in the hole in thestationary pole. Still another difliculty is that conventional straightpusher pins have a tendency to fall through the hole in the stationarycore when the electromagnet is turned over or otherwise moved about.

According to the invention, a core assembly for a tractive electromagnetis provided in which a first ferromagnetic pole is secured to one end ofa nonferromagnetic sleeve about which .acoil is wound.- A secondferromagnetic pole is mounted for movement within the sleeve. A centralhole is provided in the stationary pole to guide a nonferromagneticmember for longitudinal movement. The nonferromagnetic member is anactuating pin of nonferromagnetic material and has a flared truncatedconical end which remains within the sleeve. The ends of the poles aswell as the flared end of the actuating pin are of mating, truncated,conical shapes. Upon energization of the coil, the movable pole engagesthe conical end of the pin, driving it into engagement with the conicalend of the stationary pole. The flared conical end of the pin, being ofnonferromagnetic material, provides a residual gap between the poles topermit the movable pole to return to the normal position immediatelyupon de-energization of the coil. This type of gap is found to be veryaccurate and economical to manufacture. It is also found that theconical shape of the poles and pin permit distribution of the impact ofthe pieces over a relatively large area, thereby preventing deformationof any of the pieces of the core assembly. In tests carried out ondevices constructed according to the invention, core assemblies havebeen subjected to 20 million cycles without deformation of any of thepieces or failure of any kind. In prior devices, deformation of eitheror both the pusher pin and plunger and consequent jamming of one or theother in the hole, occurred in less than 10 million cycles and in somecases as few as 1 million cycles.

Still other advantages are obtained in practicing the invention. Noadjustment of the gap between the poles is necessary during assembly norany time thereafter since the flared, truncated, conical end of theactuating pin provides an automatically determined and easily controlledgap. The conical, gap-forming portion of the pin end also eliminates theneed to maintain close tolerances during manufacture and assembly ofvarious pieces as necessitated in previous arrangements. The flared endof the pin also limits the upward travel of the pin, preventing inertialforces from carrying the pin beyond a normal actuated position as ispossible with a straight actuating pin.

During assembly of the electromagnet still another advantage isobtained. Insertion of the pin is facilitated by the conical shape ofthe inner end of the stationary pole which tends to funnel the straightportion of the pin into the hole. Thereafter, the pin due to the flaredconical end, will not fall out of the assembly, thereby enabling theelectromagnet to be inverted and otherwise moved about.

A primary object of the invention is to reliably operate a tractiveelectromagnet over extended periods of time.

Another object of the invention is to prevent deformation of the piecesof a core assembly of a tractive electromagnet during extended operationof the electromagnet.

Another object of the invention is to arrange a core assembly for atractive electromagnet in which the residual gap is determined prior toassembly by the shape of the parts.

Another object of the invention is to provide a core assembly that isautomatically adjusted upon assembly and thereafter automatically andpermanently maintained in adjustment.

Another object is to provide a core assembly for a tractiveelectromagnet in which the necessity for maintaining close tolerancesduring manufacture and assembly is reduced.

Another object of the invention is to provide a core assembly for atractive electromagnet that may be easily assembled and thereafter movedabout without any of the pieces falling out.

In order that the invention may be practiced by others, it will bedescribed in terms of an express embodiment, given by way of exampleonly, and with reference to the accompanying drawing in which:

FIGURE 1 is a view, partially in section, of a tractive electromagnet;

FIGURE 2 is a portion of the view of FIGURE 1 shown with theelectromagnet energized;

FIGURE 3 is a partial view partially in section of a i tractiveelectromagnet known in the prior art;

FIGURE 4 is a View of the plunger and pusher pin of the electromagnet ofFIGURE 3 after extended operation.

An embodiment of the invention is shown in FIGURE 1 in which a tractiveelectromagnet 101 comprises a coil 103 wound on a thin nonferromagneticsleeve 105. A ferromagnetic pole piece 107 is driven into the sleeve tothe position shown and is held there by a knurled surface (not shown) onthe pole piece. The upper end of the pole 107 is threaded to receive anut 109. The electro- 3 magnet 101 is secured to a nonferromagneticframework 111 by means of the threaded portion of the pole 107 passingthrough a slot in the framework to hold the electromagnet between ashoulder (not shown) in the pole piece and the nut.

Prior to mounting the electromagnet on the framework, a nonferromagneticactuating or pusher pin 113 is inserted in the lower end of the sleeve.The pin is inserted with the electromagnet inverted from the positionshown in FIGURE 1. The pin falls downward, therefore, into a truncatedconical shaped hole 115 in the pole 107. The conical hole leads into acylindrical hole which passes through the pole. The hole 115 tends tofunnel the straight portion of the pin into the cylindrical hole. Aflared, truncated, conical end 117 is formed on the lower end of the pin113-. The upper conical surface of the flared end 117 mates with theconical hole 115, while the inner truncated conical surface of pin end117 mates with an external truncated conical end 119 of a erromagneticplunger 121 which is inserted into the sleeve following insertion of thepin.

In operation, the electromagnet 101 is mounted in the framework 111 inthe position shown in FIGURE 1. With the electromagnet in thede-energized state, the pusher pin 113 and plunger 121 assume theposition shown. Upon energization of the electromagnet, the plunger 121is drawn upward to a position in which the upper conical surface of thepin end 117 is in mating engagement with the conical hole 115 in thelower end of the pole 107. The pin 113 is driven therefore from theposition shown in FIGURE 1 to the position shown in FIGURE 2. In FIGURE1, the plunger end 121 and pin end 117 are shown slightly separated, andin FIG- URE 2 the plunger end, pin end and pole 107 are shown slightlyseparated. These parts are shown separated to clearly show the variousparts. In practice, however, the parts are in intimate mating contact inboth figures. When the plunger 121 is drawn upward, the upper end of thepin 113 engages the lower surface of a platform 123 extending from alever 125. The lever is pivoted at 127 and is urged CCW by a spring 128.Upon energization of the electromagnet, the pin 113 pushes the platformfrom the position shown to a position 123A, thereby driving a member129, pivoted at the left end of the lever 125, upward. Upward movementof the member 129 causes engagement of a cam with a power roll of anelectric typewriter to drive a typebar. This mechanism (not shown) iscomprised of known SCM Corporation Electric Typewriter parts and doesnot form a part of the invention herein.

In FIGURE 2, the core assembly is shown in an actuating position as aresult of the coil 103 being energized, with the pole 107, plunger 121,and pin 113 in mating engagement. The conical portion 117 of the pin,being of a nonferr-omagnetic material such as stainless steel, providesan economical and very easily controlled gap between the poles.

A prior art tractive electromagnet 301 is shown in FIGURE 3 andcomprises a conical-faced plunger 303, a conical-faced pole 304 and astraight pusher pin 305. A gap 307 of a nonferromagnetic material may beprovided by coating or otherwise securing the material on the conicalend of the pole 304. Such an arrangement, however, would necessitate anextra step in the manufaeture of the device. If the gap is of anonmetallic material, there is a further disadvantage of deteriorationunder extended use, making it difficult to control the width of the gap.Alternatively, and more commonly, the gap is of air and is obtained bycontrolling the upward movement of the plunger. One arrangement forachieving such control is by means of threads on the lower end of theplunger 303 for receiving a nut 309 which serves to stop the upwardmovement of the plunger when the nut is brought into engagement with thelower end of the sleeve 105. The nut may also be adjusted to control thewidth of the air gap. Adjustment of such a gap by this means, however,is found to be very diflicult during initial assembly and thereafter torequire periodic adjustment.

Another problem encountered with the electromagnet 301 (FIGURE 3) inwhich an air gap is used is the requirement that close tolerances bemaintained in all parts of the core assembly to prevent a tolerancebuild-up at the lower end of the electromagnet. Since this part of theelectromagnet acts as a stop for the nut 309, close tolerances arenecessary to ensure that the plunger is moved the same distancespecified in the design. Furthermore, in mass production of theelectromagnets of FIGURE 3, it is necessary to assemble the nut 309onto, the plunger 303 prior to insertion of the plunger into the sleeve10S. Consequently, the distance between the lower end of the sleeve andthe conical recess of the pole 107 must be closely controlled. Incontrast, the lower end of the electromagnet 101 (FIGURE 1) does not actas a stop for the plunger 121 so that tolerance build-up at this pointmay be neglected.

It has also been found that extended operation of the device shown inFIGURE 3 causes a mushroom deformation on the ends of either or both thepusher pin 305 and plunger 303 as indicated in FIGURE 4. Thisdeformation is due to the continual pounding of the plunger 303 againstthe lower end of the pin 305. Frequently, the deformation becomes sosevere that the pin and/ or plunger is jammed into the lower end of thepole 304, causing the pin to stick in the raised position.

From the above description other embodiments of the invention may becomeapparent. For example, the shapes of the pole faces might beinterchanged, or the actuating pin 113 could be arranged to pull ratherthan push. v

The invention claimed is:

1. A tractive electromagnet for operating a utilization devicecomprising:

(a) a coil;

(b) a first ferromagnetic pole having one end internal tosaid coil, saidend having a recess therein;

(c) a second ferromagnetic pole having one end internal to said coil;

(d) means for holding one of said poles stationary with respect to theother to permit movement of the other pole toward the stationary poleupon energization of the coil;

(e) a nonferromagnetic member positioned between the ends of the polesfor movement therebetween, said member having first and second surfacesopposite respective one ends of said poles, each said surface beingshaped for mating engagement corresponding one end of a pole;

(f) an opening defined by a third surface, said third surface being onone of said poles, and

(g) an extension secured to one of said first and second surfaces andpassing through said opening to enable operative engagement between saidmember and said utilization device in response to movement of said otherpole.

2. A tractive electromagnet according to claim wherein said one end ofsaid first pole has a conical recess therein;

said one end of said second pole has a shape complementary to saidconical recess;

each said surface of said nonfer-romagnetic member opposite a respectivepole is conically shaped for mating engagement therewith.

3. A tractive electromagnet according to claim 2 wherein said pole endsand said surfaces of said member are in the shape of truncated cones.

4. A tractive electromagnet for operating a utilization device,comprising:

(a) a coil;

(b) a first ferromagnetic pole having one end internal to said coil;

(0) a second ferromagnetic pole having one end internal to said coil;

(d) means for holding one of said poles stationary with respect to theother to permit movement of the other pole toward the stationary poleupon energization of the coil;

(e) a nonferromagnetic member in the shape of an elongated pin flared onone end and positioned between the ends of the poles for movementtherebetween, said flared end having surfaces respectively opposite oneof said one ends of the poles, each said surface being shaped for matingengagement with a respective one end of a pole; and

(f) means formed in one of said poles to engage the pin portion of saidmember to guide the member 2 lengthwise within the coil and enableoperative engagement between said pin portion of the member wherein saidone end of the first pole has a conical recess therein,

said one end of said second pole has a conical shape complementary tosaid recess,

said flared end of the elongated pin being conically shaped for matingengagement with respective opposite conically haped poles, and

said pin-engaging means formed in one of said poles is a central hole inwhich said pin member is positioned for guidance.

6. A tractive electromagnet according to claim 5 wherein said pole endsand the flared end of the pin member are in the shape of truncatedcones.

No references cited.

BERNARD A. GILHEANY, Primary Examiner. H. A. LEWITTER, AssistantExaminer.

1. A TRACTIVE ELECTROMAGNET FOR OPERATING A UTILIZATION DEVICECOMPRISING: (A) A COIL; (B) A FIRST FERROMAGNETIC POLE HAVING ONE ENDINTERNAL TO SAID COIL, SAID END HAVING A RECESS THEREIN; (C) A SECONDFERROMAGNETIC POLE HAVING ONE END INTERNAL TO SAID COIL; (D) MEANS FORHOLDING ONE OF SAID POLES STATIONARY WITH RESPECT TO THE OTHER TO PERMITMOVEMENT OF THE OTHER POLE TOWARD THE STATIONARY POLE UPON ENERGIZATIONOF THE COIL; (E) A NONFERROMAGNETIC MEMBER POSITIONED BETWEEN THE ENDSOF THE POLES FOR MOVEMENT THEREBETWEEN,